A number of infections in mammals have sufficient deleterious effects of the mammal to warrant vaccination against the particular antigen responsible for the infection. Therefore, vaccination programmes are instituted whereby the mammal is antigenically challenged with an antigen so that an immune response is elicited to confer immunity to the mammal.
Administration of the antigen to the mammal may be through a number of routes including injection intramuscularly (i.m.), subcutaneously (s.c.), or through oral administration (per os). I.m. or s.c. injection of antigen suffers from the disadvantages that relatively specialized skills are required, it is difficult to undertake on a large scale, it is expensive, and a number of side reactions can occur to either the immunizing antigen or to the emulsifying reagent in which it is presented. Oral administration of vaccines is by contrast relatively problem free except insofar as oral feeding of a number of antigens requires relatively large quantities of antigen as the amount of material that is actually absorbed and capable of stimulating an effective immune response is usually low. Thus the amount of antigen required for oral immunization generally far exceeds that required for systemic induction of immunity. There is also one major disadvantage to the oral presentation of the large quantities of antigen required to produce an antibody response and that is that feeding of these large quantities of antigen often leads to the induction of systemic tolerance (Tomasi, 1980; Mowat, 1985; Mowat and Parrot, 1983; Ngan & Kind, 1978; Hanson et al, 1979; Richman et al. 1978; Rothberg et al., 1973).
Evidence to date suggests that in general the mechanism by which antigen is take up by the small intestine, following oral feeding, is primarily via non-specific sampling of the contents of the gut lumen by "M" cells which overlie the Peyer's Patches and other lymphoid clusters of the GALT (gut-associated-lymphoid tissue) (Bland and Britton, 1984). The subsequent sensitization of local lymphocyte populations leads to the generation of local IgA Immune responses plus the sensitization of IgG suppressor cells with concomitant suppression of serum IgG responses (Tomasi, 1980; Mowat, 1985; Mowat and Parrot, 1983; Ngan & Kind, 1978; Hanson et al, 1979; Richman et al, 1978; Rothberg et al, 1973).
It is therefore apparent that the site of antigen uptake, whether it be through the Peyer's Patches or the villous epithelium, and quite probably the amount of antigen administered, dictates the type of immune response generated by orally administered antigen. The question arises then as to whether there are any other antigens apart from cholera toxin which exhibit the ability to specifically prime the mucosal immune system upon oral challenge and/or to stimulate the humoral immune response in a dose dependant manner without inducing systemic tolerance and without the need for excessive doses of antigen.
With this view in mind we decided to investigate the possible potential of certain adhesive molecules, which have been implicated in the initial attachment of a number of intestinal pathogens, to stimulate the immune response when orally administered. These surface antigens which confer adhesive properties to a number of strains of enterotoxigenic E. coli (ETEC) have been identified as nonflagellar, filamentous proteinaceous appendages, or pili (Gaastra & de Graaf, 1982). Examples include the CFA I and CFA II antigens of human ETEC strains and the K88, K99, F41 and 987P pili of animal ETEC strains (Gibbons et al, 1975; Evans & Evans, 1978; Levine et al., 1980; Morgan et al., 1978; de Graaf & Roorda, 1982). In addition, we have examined the ability of a number of other proteins which have no apparent role in colonization to prime the immune system upon oral feeding. These antigens included a number of lectins a serotypic antigen of S. typhimurium (the type "i"flagella), inactivated flu virus and S. typhimurium endotoxin (LPS). Oral priming was compared to the response generated to wholly intramuscular challenge (i.m.).
Thus, the aim of these studies was to provide a method whereby the uptake of an immunogen or antigen by the gastrointestinal tract mucosa is improved to the extract that it is possible to elicit serum and secretory antibodies by oral feeding of low doses of the immunogen without the induction of oral tolerance.
Accordingly the invention describes a group of molecules (mucosal immunogens) which when fed lead to the production of serum antibodies to these proteins at comparable levels to those obtained by intramuscular injection of these molecules. Furthermore when larger quantities of these actigens are fed there is a concomitant stimulation of the production of mucosal antibodies to the immunizing molecules.
In a further aspect of this invention a process is described whereby the antibody response generated to the orally fed molecules can be augmented or changed by the co-feeding of a number of dietary molecules.
In another aspect of this invention a process is described whereby a hapten or protein can be coupled to a mucosal immunogen and the complex of which, when fed, results in the production of antibodies to the hapten or coupled protein.
______________________________________ ABBREVIATIONS ______________________________________ 1. Ab Antibody 2. BSA bovine serum albumin 3. ConA Conconavlin A 4. DNP dinitrophenyl 5. ELISA Enzyme linked immunosorbent assay 6. ETEC enterotoxigenic E. coli 7. GALT gut associated lympnhoid tissue 8. HA hydroxy apatite 9. im intra muscular 10. LHRH luteinizing hormone releasing hormone. 11. LPS lipopolysaccharide 12. LT-B neat labile toxin of enterotoxigenic E. coli. 13. O/N overnight 14. per oo oral administration 15. ps polysaccharide 16. RT room temperature 17. sc subcutaneous 18. SDS-PAGE SDS-polyacrylamide gel electrophonesis 19. TCA trichloracetic acid. ______________________________________